The last glacial maximum (21,000 yr before present) is the most recent time period with a global mean temperature change of similar magnitude, but opposite sign to that predicted for the year 2100. The global cooling of around 4C is mostly explained by a combination of additional ice-sheets covering parts of North America and Europe and lower concentrations of carbon dioxide. Many other aspects of the Earth System were also radically altered compared to the pre-industrial, including vegetation, aerosols and the methane cycle. In this talk I will show Earth System model simulations of the LGM with the CMIP5 model HadGEM2-ES in which we aimed at evaluating the changes in these systems during this time period. I will also briefly cover using these Earth System components as constraints on mechanisms of ice-age abrupt climate events such as Dansgaard-Oeschger events.